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C T Russell - One of the best experts on this subject based on the ideXlab platform.
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foreshock cavitons for different Interplanetary Magnetic Field geometries simulations and observations
Journal of Geophysical Research, 2011Co-Authors: X Blancocano, N. Omidi, P Kajdic, C T RussellAbstract:[1] Global hybrid (kinetic ions, fluid electrons) simulations have shown the existence of foreshock cavitons characterized by large depressions in plasma density and Magnetic Field magnitude, bounded by enhancements in these two parameters. Foreshock cavitons share some characteristics with reported foreshock cavities, but in contrast to the cavities that often appear as isolated structures, cavitons are always found surrounded by a sea of ultra low frequency (ULF) waves. They always occur in regions deep in the foreshock, downstream from the ion and ULF wave boundaries. We perform global hybrid simulations to show that cavitons can form for a variety of Interplanetary Magnetic Field (IMF) geometries and different solar wind Mach numbers. We use Cluster data to show that cavitons are a common foreshock feature, and that they can form for different IMF orientations, consistent with our simulation results. We find that cavitons show density and Field decrements as large as 60% of the ambient values. They are immersed in regions where waves show transverse and compressive components and the presence of diffuse ion distributions. We use linear kinetic theory to estimate wave growth for the two types of waves responsible for caviton formation, i.e., the weakly compressive waves and oblique propagating linearly polarized waves. Some of the cavitons observed by Cluster show trains of high-frequency waves inside them and this is consistent with the predictions of local higher-resolution hybrid simulations.
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global hybrid simulations foreshock waves and cavitons under radial Interplanetary Magnetic Field geometry
Journal of Geophysical Research, 2009Co-Authors: X Blancocano, N. Omidi, C T RussellAbstract:[1] We use global hybrid (kinetic ions and fluid electrons) simulations to study the solar wind interaction with the magnetosphere for a radial (θvB = 0) Interplanetary Magnetic Field (IMF) geometry. Global hybrid simulations provide a collective picture of processes taking place in the foreshock, bow shock, and magnetosheath. Because ions are treated as particles, these codes also give information on ion-scale microphysics. Under radial IMF geometry, the foreshock forms in front of the dayside magnetosphere, and the plasma convecting downstream is very perturbed. The foreshock is permeated by weakly compressive ultralow frequency (ULF) waves that propagate at angles up to 30° to the ambient Field. These weakly compressive waves are generated by Field-aligned ions. Wave-Particle interaction results in ion scattering, while wave amplitude grows and fluctuations become compressive as they approach the shock. While weakly compressive waves are dominant far from the shock, a second population of ULF fluctuations arises close to it. These fast magnetosonic waves propagate at large angles to the Magnetic Field and are linearly polarized. We find that, in addition to the ULF waves, large depressions in density and Magnetic Field magnitude form near the shock. These density cavitons or depressions are bounded by enhanced Magnetic Fields, and inside them, hot diffuse ions are present. Foreshock density cavitons in our simulations are embedded in regions with ULF activity, which is in contrast to the isolated character of “foreshock cavities” reported previously. We show that density cavitons form due to the nonlinear interaction of the two types of waves present in the foreshock. Wave interaction also modifies the characteristics of weakly compressive waves. A comparison of our results with Cluster observations reveals that the characteristics of weakly compressive waves in our simulation resemble the properties of right-handed 30-s waves found in the terrestrial foreshock. Likewise, we show the existence of density cavitons, or depressions, in regions of Earth's foreshock permeated by ULF waves. The properties of these observed Cluster cavitons are similar to the ones we find in the simulations.
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an advanced approach to finding magnetometer zero levels in the Interplanetary Magnetic Field
Measurement Science and Technology, 2008Co-Authors: H K Leinweber, C T Russell, K Torkar, T L Zhang, V AngelopoulosAbstract:For a magnetometer that measures weak Interplanetary Fields, the in-flight determination of zero levels is a crucial step of the overall calibration procedure. This task is more difficult when a time-varying Magnetic Field of the spacecraft interferes with the surrounding natural Magnetic Field or when the spacecraft spends only short periods of time in the Interplanetary Magnetic Field. Thus it is important to examine the algorithms by which these zero levels are determined, and optimize them. We find that the method presented by Davis and Smith (1968 EOS Trans. AGU 49 257) has significant mathematical advantages over that published by Belcher (1973 J. Geophys. Res. 71 5509) as well as over the correlation technique published by Hedgecock (1975 Space Sci. Instrum. 1 83–90). We present an alternative derivation of the Davis–Smith method which illustrates that it is also a correlation technique. It also works with first differences as well as filtered data as input. In contrast to the postulate by Hedgecock (1975 Space Sci. Instrum. 1 83–90), we find that using first differences in general provides no advantage in determining the zero levels. Our new algorithm obtains zero levels by searching for pure rotations of the Interplanetary Magnetic Field, with a set of sophisticated selection criteria. With our algorithm, we require shorter periods (of the order of a few hours, depending on solar wind conditions) of Interplanetary data for accurate zero level determination than previously published algorithms.
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possible distortion of the Interplanetary Magnetic Field by the dust trail of comet 122p de vico
The Astrophysical Journal, 2003Co-Authors: C T Russell, G H Jones, A Balogh, M K DoughertyAbstract:Interplanetary Field enhancements are unexplained localized increases in the heliospheric Magnetic Field magnitude. Four such enhancements, detected by the Pioneer Venus Orbiter and Ulysses spacecraft, have been found to be very close to the orbital plane of comet 122P/de Vico. Analysis of the Magnetic Field during these events reveals that the Field perturbations were close to those expected if the Interplanetary Magnetic Field draped at the comet's orbit and that the Field enhancements represent crossings of a sheet of disturbed solar wind in the comet's orbital plane. The results suggest that a dense dust stream may occupy at least part of the orbit of de Vico and that its effects on the solar wind are apparent almost 1.4 AU downstream. One Field enhancement suggests the existence of an annulus of dust extending sunward of the dust trail itself.
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reconnection at the high latitude magnetopause during northward Interplanetary Magnetic Field conditions
Journal of Geophysical Research, 2001Co-Authors: T G Onsager, J D Scudder, Mike Lockwood, C T RussellAbstract:The Polar spacecraft had a prolonged encounter with the high-latitude dayside magnetopause on May 29, 1996. This encounter with the magnetopause occurred when the Interplanetary Magnetic Field was directed northward. From the three-dimensional electron and ion distribution functions measured by the Hydra instrument, it has been possible to identify nearly all of the distinct boundary layer regions associated with high-latitude reconnection. The regions that have been identified are (1) the cusp; (2) the magnetopause current layer; (3) magnetosheath Field lines that have interconnected in only the Northern Hemisphere; (4) magnetosheath Field lines that have interconnected in only the Southern Hemisphere; (5) magnetosheath Field lines that have interconnected in both the Northern and Southern Hemispheres; (6) magnetosheath that is disconnected from the terrestrial Magnetic Field; and (7) high-latitude plasma sheet Field lines that are participating in magnetosheath reconnection. Reconnection over this time period was occurring at high latitudes over a broad local-time extent, interconnecting the magnetosheath and lobe and/or plasma sheet Field lines in both the Northern and Southern Hemispheres. Newly closed boundary layer Field lines were observed as reconnection occurred first at high latitudes in one hemisphere and then later in the other. These observations establish the location of magnetopause reconnection during these northward Interplanetary Magnetic Field conditions as being at high latitudes, poleward of the cusp, and further reinforce the general interpretation of electron and ion phase space density signatures as indicators of Magnetic reconnection and boundary layer formation.
J B H Baker - One of the best experts on this subject based on the ideXlab platform.
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Field aligned current reconfiguration and magnetospheric response to an impulse in the Interplanetary Magnetic Field by component
Geophysical Research Letters, 2013Co-Authors: F D Wilder, M R Hairston, S Eriksson, H Korth, J B H Baker, C J Heinselman, B J AndersonAbstract:[1] When the Interplanetary Magnetic Field (IMF) is dawnward or duskward, Magnetic merging between the IMF and the geoMagnetic Field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the Defense Meteorological Satellite Program spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawnside FAC pair. We find there is a delay of approximately 1.25 h between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvenic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.
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polar cap electric Field saturation during Interplanetary Magnetic Field bz north and south conditions
Journal of Geophysical Research, 2010Co-Authors: F D Wilder, C R Clauer, J B H BakerAbstract:[1] We report the results of an investigation of the saturation of the polar cap electric Field during periods of large northward and southward Interplanetary Magnetic Field (IMF). While it has been demonstrated that saturation can occur for both northward and southward IMF, a direct comparison between the two regimes during saturated driving has not been performed. We use solar wind measurements to search for events between 1998 and 2007 when the IMF is stable for 50 min. The selected intervals are binned according to Interplanetary electric Field (-V sw × B). SuperDARN Doppler radar velocity vectors from high-latitude antisunward looking beams are averaged to determine the approximate polar cap electric Field. Results show that sunward convection under northward IMF is stronger in summer than in winter, but that antisunward convection under southward IMF exhibits the opposite seasonal behavior. One explanation is that, as the earth tilts near solstice, lobe reconnection is less effective in the winter hemisphere.
M F Thomsen - One of the best experts on this subject based on the ideXlab platform.
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high speed solar wind with southward Interplanetary Magnetic Field causes relativistic electron flux enhancement of the outer radiation belt via enhanced condition of whistler waves
Geophysical Research Letters, 2013Co-Authors: Ryuho Kataoka, M F Thomsen, Yoshiya Kasahara, Atsushi Kumamoto, T NagaiAbstract:[1] Relativistic electron flux in the outer radiation belt tends to increase during the high-speed solar wind stream (HSS) events. However, HSS events do not always cause large flux enhancement. To determine the HSS events that cause such enhancement and the mechanisms that are responsible for accelerating the electrons, we analyzed long-term plasma data sets, for periods longer than one solar cycle. We demonstrate that during HSS events with the southward Interplanetary Magnetic Field (IMF)-dominant HSS (SBz-HSS), relativistic electrons are accelerated by whistler mode waves; however, during HSS events with the northward IMF-dominant HSS, this acceleration mechanism is not effective. The differences in the responses of the outer radiation belt flux variations are caused by the differences in the whistler mode wave–electron interactions associated with a series of substorms. During SBz-HSS events, hot electron injections occur and the thermal plasma density decreases due to the shrinkage of the plasmapause, causing large flux enhancement of relativistic electrons through whistler mode wave excitation. These results explain why large flux enhancement of relativistic electrons tends to occur during SBz-HSS events.
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Interplanetary Magnetic Field control of afternoon sector detached proton auroral arcs
Journal of Geophysical Research, 2002Co-Authors: J L Burch, W S Lewis, T J Immel, P C Anderson, H U Frey, S A Fuselier, Jeanclaude Gerard, S B Mende, D G Mitchell, M F ThomsenAbstract:[1] Data from the Far Ultraviolet Imager (FUV) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite show that subauroral proton arcs appear in the afternoon sector during geoMagnetically disturbed periods when the Interplanetary Magnetic Field rotates either from south to north or from west to east and when the magnetosphere is moderately compressed. Time series of proton aurora images show that the proton emissions are generally aligned along the equatorward part of the auroral oval. However, when Interplanetary Magnetic Field (IMF) Bz changes from negative to positive the auroral oval contracts toward higher latitudes while the ring current proton precipitation remains stationary, resulting in a separation of several degrees between the latitude of the new oval position and a subauroral proton arc in the afternoon sector. A similar effect occurs when IMF By rotates from negative to positive, in which case the oval in the afternoon sector retreats toward higher latitudes, again leaving a separation between the oval and the subauroral proton arc of several degrees. Comparisons with low-altitude and geosynchronous satellite data show that the subauroral proton arc is caused by the precipitation of protons with energies from several keV to 30 keV and is likely associated with the existence of a plasmaspheric “drainage plume.” In contrast, the proton emissions along the main oval are caused by protons with energies generally less than 10 keV.
F D Wilder - One of the best experts on this subject based on the ideXlab platform.
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Field aligned current reconfiguration and magnetospheric response to an impulse in the Interplanetary Magnetic Field by component
Geophysical Research Letters, 2013Co-Authors: F D Wilder, M R Hairston, S Eriksson, H Korth, J B H Baker, C J Heinselman, B J AndersonAbstract:[1] When the Interplanetary Magnetic Field (IMF) is dawnward or duskward, Magnetic merging between the IMF and the geoMagnetic Field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the Defense Meteorological Satellite Program spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawnside FAC pair. We find there is a delay of approximately 1.25 h between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvenic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.
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polar cap electric Field saturation during Interplanetary Magnetic Field bz north and south conditions
Journal of Geophysical Research, 2010Co-Authors: F D Wilder, C R Clauer, J B H BakerAbstract:[1] We report the results of an investigation of the saturation of the polar cap electric Field during periods of large northward and southward Interplanetary Magnetic Field (IMF). While it has been demonstrated that saturation can occur for both northward and southward IMF, a direct comparison between the two regimes during saturated driving has not been performed. We use solar wind measurements to search for events between 1998 and 2007 when the IMF is stable for 50 min. The selected intervals are binned according to Interplanetary electric Field (-V sw × B). SuperDARN Doppler radar velocity vectors from high-latitude antisunward looking beams are averaged to determine the approximate polar cap electric Field. Results show that sunward convection under northward IMF is stronger in summer than in winter, but that antisunward convection under southward IMF exhibits the opposite seasonal behavior. One explanation is that, as the earth tilts near solstice, lobe reconnection is less effective in the winter hemisphere.
A. V. Suvorova - One of the best experts on this subject based on the ideXlab platform.
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magnetopause expansions for quasi radial Interplanetary Magnetic Field themis and geotail observations
arXiv: Space Physics, 2013Co-Authors: A. V. Suvorova, Jih-hong Shue, K L Ackerson, David G. Sibeck, J.p. Mcfadden, A. V. Dmitriev, H. Hasegawa, Karel JelinekAbstract:We report THEMIS and Geotail observations of prolonged magnetopause (MP) expansions during long-lasting intervals of quasi-radial Interplanetary Magnetic Field (IMF) and nearly constant solar wind dynamic pressure. The expansions were global: the magnetopause was located more than 3 RE and ~7 RE outside its nominal dayside and magnetotail locations, respectively. The expanded states persisted several hours, just as long as the quasi-radial IMF conditions, indicating steady-state situations. For an observed solar wind pressure of ~1.1-1.3 nPa, the new equilibrium subsolar MP position lay at ~14.5 RE, far beyond its expected location. The equilibrium position was affected by geoMagnetic activity. The magnetopause expansions result from significant decreases in the total pressure of the high-beta magnetosheath, which we term the low-pressure magnetosheath (LPM) mode. A prominent LPM mode was observed for upstream conditions characterized by IMF cone angles less than 20 ~ 25 grad, high Mach numbers and proton plasma beta<1.3. The minimum value for the total pressure observed by THEMIS in the magnetosheath adjacent to the magnetopause was 0.16 nPa and the fraction of the solar wind pressure applied to the magnetopause was therefore 0.2, extremely small. The equilibrium location of the magnetopause was modulated by a nearly continuous wavy motion over a wide range of time and space scales.
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magnetopause expansions for quasi radial Interplanetary Magnetic Field themis and geotail observations
Journal of Geophysical Research, 2010Co-Authors: A. V. Suvorova, Jih-hong Shue, K L Ackerson, David G. Sibeck, J.p. Mcfadden, A. V. Dmitriev, H. Hasegawa, Karel JelinekAbstract:[1] We report Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geotail observations of prolonged magnetopause (MP) expansions during long-lasting intervals of quasi-radial Interplanetary Magnetic Field (IMF) and nearly constant solar wind dynamic pressure. The expansions were global: The magnetopause was located more than 3 RE and ∼7 RE outside its nominal dayside and magnetotail locations, respectively. The expanded states persisted several hours, just as long as the quasi-radial IMF conditions, indicating steady state situations. For an observed solar wind pressure of ∼1.1–1.3 nPa, the new equilibrium subsolar MP position lay at ∼14.5 RE, far beyond its expected location. The equilibrium position was affected by geoMagnetic activity. The magnetopause expansions result from significant decreases in the total pressure of the high-β magnetosheath, which we term the low-pressure magnetosheath (LPM) mode. A prominent LPM mode was observed for upstream conditions characterized by IMF cone angles less than 20°–25°, high Mach numbers and proton plasma β ≤ 1.3. The minimum value for the total pressure observed by THEMIS in the magnetosheath adjacent to the magnetopause was 0.16 nPa and the fraction of the solar wind pressure applied to the magnetopause was therefore 0.2, extremely small. The equilibrium location of the magnetopause was modulated by a nearly continuous wavy motion over a wide range of time and space scales.
